Schottky barrier diodes have long been used as infrared detectors because their low energy barrier height property was suitable for IR detection. In addition, because of their fabrication process compatibility to the existing CMOS process, it is possible to integrate other readout circuitry with the multiple detector elements arranged in a pixel array. Unlike other p-n junction photodiodes where most of photo-generation of carriers induced by light absorption takes place in the bulk substrate, the photo-generation of carriers in Schottky barrier diodes takes place on the metal surface governed by the thermionic emission. If carriers in the metal get enough thermal energy induced by light absorption they can emit from the metal surface by overcoming the binding energy which is called the work function of the metal. If the potential barrier of the metal-semiconductor junction is lower than the energy that the emitted carrier has, an electric current flows across the SB junction.
The quantum efficiency of these Schottky barrier diodes is inherently very low due to their thermionic emission nature. This is because incident light passes through only once and only a portion of the light is absorbed by the thin metal layer. Accordingly, infrared sensors having higher quantum efficiency are required.